Phthalocyanine compounds have superior thermal and chemical stability by its structural characteristics, and changeable absorption property by metallic element introduced in the center of compound structure or characteristic group substituted at outer of compound structure. Thus, the phthalocyanine compounds are being applied in various fields such as pigments for CD, pigments applied in organic photo conductor for laser print, near-infrared absorption pigments of near-infrared absorption filter for display such as PDP (plasma display), pigments for solar cell, and so on, as well as pigments as a specific purpose. Recently, among the applications, the usage as near-infrared absorption pigments of near-infrared absorption filter for PDP is sharply increasing by rapid expansion of the display industry.
A near-infrared absorption pigment for PDP must have high light absorption property in the region of 800 to 950 nm, and low light absorption property in the visible light region, namely high transmittance, to improve color gamut (color reproductivity) of display devices. As the near-infrared absorption pigment, not only phthalocyanine compound but also various compounds such as cyanine based compounds, nickel-dithionyl based compounds, diimonium based compounds and so on, can be used. However, the cyanine based compounds are difficult to be applied actually because of lack of heat resistance, and the diimonium based compounds are limited in application because of lack of durability to the environment such as moisture, and not suitable for the near-infrared absorption filter of coating type which is being used recently. Also, the nickel-dithionyl based compounds are mainly used as sub materials, not as main materials, because of low solubility, even though they have an advantage of low light absorption property in the visible light region.
Phthalocyanine compounds have superior characteristics in all respects of durability, weather resistance and solubility, and high absorptivity in the maximum absorption wavelength of the near-infrared light region. Therefore, the phthalocyanine compounds are especially useful as a coating type near-infrared absorption pigment for PDP, and being used in various uses. Conventional phthalocyanine compounds have superior photosensitive characteristic in the region of 900 to 1000 nm, but light absorptivity in the visible light region is higher than nickel-dithionyl based compounds and so on, and light absorptivity in the region of 800 to 900 nm and the region of long wavelength over 1000 nm is not enough. Recently, the maximum absorption wavelength of the phthalocyanine compound is shifted to long wavelength region by using various central metals, but the light absorption in the region of 800 to 900 nm is insufficient. Moreover, in the case that a substituent such as a phenol, a thiophenol, first amine, and so on is introduced to shift the maximum absorption wavelength to long wavelength region or the region of 800 to 900 nm, the light absorptivity in the visible light region is increased, thus, visible light transmittance and color gamut are decreased, and applications are limited.